Method and device for continuously casting strip cast piece

ABSTRACT

In a method of manufacturing a plurality of coil-shaped thin cast strips while molten metal r is being supplied to the molten metal pool  3  formed by a pair of cooling drums  1, 1  and a pair of side dams, when a casting operation corresponding to one coil of the coil-shaped thin cast strip has been completed, gas is made to blow from the gas nozzles  7   b  toward the scum s floating on the molten metal, so that the scum s drifts, due to the gas flow to one meniscus m 2 , and the thus drifted scum is attached to a surface of the cast strip and circumferential faces of the cooling drums and is then discharged from the molten metal pool.

TECHNICAL FIELD

[0001] The present invention relates to a method and machine formanufacturing thin cast strips, 1 to 10 mm thick, by means of continuouscasting. More particularly, the present invention relates to thedischarge processing of scum floating on a molten metal surface in amolten metal pool.

BACKGROUND ART

[0002] As a method for manufacturing thin cast strips by means ofcontinuous casting, there is provided a twin drum type continuouscasting method described as follows. While molten metal is beingsupplied to a molten metal pool formed by a pair of cooling drums, whichare rotated in the opposite direction to each other, and by a pair ofside dams which are pressed against both end faces of these coolingdrums, solidified shells are formed on the circumferential faces of therespective cooling drums which are being rotated, and the thus formedsolidified shells are compressed to each other at the kissing pointformed between the cooling drums so that the solidified shells areformed into a thin cast strip, which is wound into a coil on thedownstream side.

[0003] Non-metallic inclusions such as slag are mixed in the moltenmetal supplied to the molten metal pool. Further, on a surface of themolten metal, metallic oxides are generated by oxidation. The thusgenerated non-metallic inclusions and metallic oxides are formed into ascum floating on the surface of the molten metal in the molten metalpool and caught from the meniscuses by the circumferential faces of thecooling drums and onto the surface of the cast strip. As a result, inthe portion into which the scum has been caught, cooling of the caststrip is delayed and, further, the cast strip can not be cooleduniformly. Accordingly, problems such as cracks, non-uniformity ofstructure and unevenness of acid pickling are caused. Further,unevenness of gloss is caused on products.

[0004] As a method of preventing the surface of molten metal in themolten metal pool from being oxidized, there is conventionally provideda method in which the molten metal pool is covered with a seal chamber,and non-oxidizing gas such as inert gas is supplied into the sealchamber so as to seal the molten metal face. This method is disclosed,for example, in Japanese Unexamined Patent Publication No. 3-198951.However, even when the molten metal face is sealed by this method, it isimpossible to sufficiently prevent the generation and formation of scum.

[0005] On the other hand, as a method of preventing scum from beingcaught onto the circumferential faces of the drums and onto the surfaceof the cast strip, there is provided a conventional method in which apair of scum dams extending in the width direction of the drums arearranged on both sides of a molten metal pouring nozzle being dipped inthe molten metal so that the flow of scum to the cooling drum side canbe prevented by the scum dams. This technique is disclosed, for example,in Japanese Unexamined Patent Publication No. 3-66450. However, evenwhen the scum dams are provided as described above, it is impossible toprevent scum, which has been generated and formed in the periphery ofthe meniscus between the scum dams and the cooling drums, from beingcaught by the surfaces of the drums.

[0006] Especially, it is a problem that the scum is unevenly caught inthe width direction of the cast strip. When a quantity of scum is large,there is a tendency that the scum is unevenly caught. When the castingtime increases, the quantity of scum generated and formed is increased.Therefore, in the case where casting work is performed over a longperiod of time so as to enhance the productivity, the quantity of scumgenerated and formed is increased and the thus generated and formed scumtends to be unevenly caught.

SUMMARY OF THE INVENTION

[0007] It is a task of the present invention to prevent scum from beingcaught by the circumferential faces of drums and onto a surface of acast strip by discharging scum floating in a molten metal pool from themolten metal pool in a method of manufacturing thin cast strips by meansof continuous casting.

[0008] In order to solve the above problems,

[0009] (1) the present invention provides a continuous casting methodfor manufacturing thin cast strips, in which a pair of scum damsextending in a drum width direction arranged on both sides of a moltenmetal pouring nozzle are arranged by being dipped in molten metal inmolten metal pool formed by a pair of cooling drums and a pair of sidedams, a thin cast strip is cast while molten metal is being suppliedinto the molten metal pool, and the thin cast strip is wound into a coilso as to manufacture a plurality of coil-shaped thin cast strips, thecontinuous casting method for manufacturing thin cast strips comprisingthe step of pulling up the scum dams from the molten metal when castingwork, corresponding to one coil of the thin cast strip, is completed.

[0010] (2) The present invention provides another continuous castingmethod for manufacturing thin cast strips, in which a thin cast strip iscast while molten metal is being supplied into a molten metal poolformed by a pair of cooling drums and a pair of side dams, and the thincast strip is wound into a coil so as to manufacture a plurality ofcoil-shaped thin cast strips, the continuous casting method formanufacturing thin cast strips comprising the step of blowing gas onto amolten metal face in the molten metal pool toward one of the pair ofcooling drums or both of the pair of cooling drums when the castingwork, corresponding to one coil of the thin cast strip, is completed.

[0011] In order to solve the above problems,

[0012] (3) the present invention provides a continuous casting machinefor manufacturing thin cast strips, in which a thin cast strip is castwhile molten metal is being supplied into a molten metal pool formed bya pair of cooling drums and a pair of side dams, and the thin cast stripis wound into a coil so as to manufacture a plurality of coil-shapedthin cast strips, the continuous casting machine for manufacturing thincast strips comprising gas nozzles to blow gas, which are arranged at anupper central portion of the molten metal pool, being directed towardone or both of the pair of cooling drums, to a molten metal face of themolten metal pool when casting operation corresponding to one coil ofthe thin cast strip has been completed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a sectional side view for explaining an embodimentaccording to claim 1 of the invention. FIG. 1(a) is a view showing astate in which continuous casting is steadily performed, and FIG. 1(b)is a view showing a state in which scum is discharged.

[0014]FIG. 2 is a sectional side view for explaining an embodimentaccording to claims 2 and 3 of the invention. This view shows a mode inwhich scum is discharged.

[0015]FIG. 3 is a plan view of FIG. 2.

[0016]FIG. 4 is a sectional side view for explaining another embodimentaccording to claims 2 and 3 of the invention. This view shows a mode inwhich scum is discharged.

[0017]FIG. 5 is a plan view of FIG. 4.

THE MOST PREFERRED EMBODIMENT

[0018] An embodiment of the present invention, in which a twin drum typecontinuous casting machine is used, will be explained as follows. FIGS.1(a) and 1(b) are sectional side views for explaining an embodimentaccording to claim 1 of the invention.

[0019] A pair of side dams 2, 2 are pressed against both end faces of apair of cooling drums 1, 1 which are rotated in the opposite directionto each other.

[0020] In the view, only one of the pair of side dams 2, 2 is shown by avirtual line. Therefore, the molten metal pool 3 is formed by the pairof cooling drums 1, 1 and the pair of side dams 2, 2.

[0021] Molten metal r is supplied from a tundish (not shown) into themolten metal pool 3 via the molten metal pouring nozzle 4. An upperportion of the molten metal pool 3 is covered with a seal chamber (notshown) for preventing the generation and formation of scum caused when asurface of molten metal is oxidized, and non-oxidizing gas such as argonor nitrogen is supplied into the seal chamber.

[0022] Molten metal r in the molten metal pool 3 is cooled by thecircumferential faces of the pair of cooling drums 1, 1, and a pair ofsolidified shells g, g are formed. The pair of solidified shells g, gare compressed at the kissing point kp of the drum and are formed intothe thin cast strip c and then moved downward.

[0023] The thin cast strip c is wound by a coiler (not shown), which isarranged on the downstream side, into a coil. When the weight of thethus wound thin cast strip has reached a predetermined value, thewinding operation is stopped and the thin cast strip c is successivelywound by another coiler. In this way, a plurality of coil-shaped thincast strips are manufactured.

[0024] A non-oxidizing gas such as argon or nitrogen is supplied intothe seal chamber that covers the upper portion of the molten metal pool3 so as to prevent the generation and formation of scum which isgenerated and formed by oxidation of the surface of molten metal,however, it is impossible to sufficiently prevent the generation andformation of scum.

[0025] In order to prevent the scum from being caught on the surface ofthe cast strip, as shown in FIG. 1(a), there are provided a pair of scumdams 5, 5 extending in the drum width direction being arranged on bothsides of the molten metal pouring nozzle 4, and the pair of scum dams 5,5 are dipped in molten metal, so that the scum s floating on the moltenmetal surface can be prevented from flowing to the drum side.

[0026] In the process of casting, from the sectional size of the caststrip, specific gravity of the cast strip and the casting speed, theweight of the thin cast strip, which has been moved from the kissingpoint kp of the twin drums, is calculated in real time.

[0027] When the thus calculated weight has reached a weightcorresponding to one coil and casting operation per one coil has beencompleted, the pair of scum dams 5, 5 are pulled up from the moltenmetal as shown in FIG. 1(b).

[0028] After the scum dams 5, 5 have been pulled up, scum s floating onthe molten metal surface is made to flow to the cooling drum side by acurrent of molten metal and it drifts to the meniscuses m.

[0029] At this time, as the cooling drums are continuously rotated, thescum s which has drifted to the meniscuses m is caught by thecircumferential faces of the drums and by the surface of the cast strip,and discharged from the molten metal pool 3.

[0030]FIGS. 2 and 3 are sectional side views for explaining anembodiment according to claims 2 and 3 of the invention. Like referencecharacters are used to indicated like parts in FIG. 1. In an upperportion of the molten metal pool 3, there is provided a seal chamber(not shown), which is supplied with non-oxidizing gas.

[0031] In the view, there is shown a mode in which the pair of scum dams5, 5 are pulled up from the molten metal. However, in the process ofcasting, the pair of scum dams 5, 5 are dipped in the molten metal r, sothat the molten metal r can be prevented from flowing to the meniscusesm1 and m2.

[0032] On the back faces of the scum dams 5, 5, there are provided gasnozzles 6 a and 6 b for blowing non-oxidizing gas to the molten metal inthe molten metal pool, wherein the gas nozzles 6 a and 6 b are directedfrom the sides of the meniscuses m1 and m2 to the molten metal pouringnozzle 4.

[0033] Concerning the type of the gas nozzles 6 a and 6 b, any type gasnozzles such as slit type gas nozzles or circular hole type gas nozzlesmay be used. In the case of the slit type gas nozzle, the dimensions ofan exemplary nozzle are described as follows. The width is 1.5 mm, thelength is 18 mm, the distance to the molten metal face is 60 to 70 mm(in the case where the scum dams are being dipped in molten metal).

[0034] In the case of the circular hole type gas nozzle, the dimensionsof an exemplary nozzle are described as follows. The nozzle diameter is0.5 to 1.0 mm, the hole pitch is 5 mm and the distance to the moltenmetal face is 80 mm.

[0035] The height of the gas nozzle and the injection angle can beadjusted according to the height of the molten metal face. The rate offlow is 20 to 30 mps in the case of the slit type nozzle and of thecircular hole type nozzle.

[0036] In the same manner as that of FIG. 1, in FIGS. 2 and 3, the thincast strip c is wound by a coiler (not shown), which is arranged on thedownstream side, into a coil-shape. When the weight of the thus woundthin cast strip has reached a predetermined value, the winding operationis stopped and the thin cast strip c is successively wound by anothercoiler (not shown).

[0037] In this way, a plurality of coil-shaped thin cast strip aremanufactured.

[0038] In the process of continuous casting, the scum dams 5, 5 aredipped in the molten metal r in the molten metal pool 3 so that theflows of scums to the meniscuses m1 and m2 are blocked and scum s isprevented from being caught on the circumferential faces of the drumsand the surface of the cast strip. From the gas nozzles 6 a and 6 b,non-oxidizing gas such as nitrogen or argon is blown out from thecircumferential faces of the drums, before the meniscuses m1 and m2, andtoward the scum dams 5.

[0039] Therefore, the scum floating between the scum dam 5 and themeniscuses ml and m2 is blown by gas to the scum dam 5 and, further,blown to the side dams. In this way, the scum is prevented from beingcaught by the meniscuses m1 and m2.

[0040] In the process of casting, from the sectional size of the caststrip, the specific gravity of the cast strip and the casting speed, theweight of the thin cast strip, which has been moved from the kissingpoint kp of the twin drums, is calculated in real time. When the thuscalculated weight has reached a weight corresponding to one coil and acasting operation for one coil has been completed, the pair of scum dams5, 5 are pulled up from the molten metal as shown in FIG. 2. At the sametime, from one gas nozzle 6 b, which the right gas nozzle in the caseshown in the drawing, of the gas nozzles 6 a, 6 b, non-oxidizing gas isblown out.

[0041] The scum s floating on the molten metal surface drifts from onemeniscus m1 to the other meniscus m2. As the cooling drums 1, 1 aresuccessively rotated at this time, the scum s which has drifted to themeniscus m2 is caught on the circumferential faces of the drums and thesurface of the cast strip and discharged from the molten metal pool 3.

[0042] In this connection, in this embodiment, the gas nozzles 6 a, 6 bare attached to the scum dams 5, however, the gas nozzles 6 a, 6 b maybe arranged separate from the scum dams 5.

[0043]FIGS. 4 and 5 are views showing another embodiment according toclaims 2 and 3. Different points of this embodiment from the embodimentshown in FIGS. 2 and 3 are described as follows. In the embodiment shownin FIGS. 2 and 3, gas is made to blow out to only one of the meniscuses,however, in this embodiment shown in FIGS. 4 and 5, gas is made to blowout to both meniscuses.

[0044] On both sides of the molten metal pouring nozzle 4, there areprovided gas nozzles 6 c, 6 d from which gas is made to blow out fromthe central portion of the molten metal pool 3 to both meniscuses m, m.

[0045] In the same manner as that shown in FIGS. 2 and 3, in the methodof manufacturing a plurality of coil-shaped thin cast strips, when thecalculated weight of a cast strip has reached a value corresponding tothe weight of one coil and a casting operation of one coil has beencompleted, the scum dams 5, 5 are pulled up from molten metal r andnon-oxidizing gas is made to blow out from the gas nozzles 6 c, 6 d.

[0046] When non-oxidizing gas blows out as described above, the scum sfloating on the molten metal surface drifts, due to the non-oxidizinggas flow, toward both meniscuses m, m.

[0047] In the same manner as that described before, as the cooling drums1, 1 are successively rotated at this time, the scum s, which hasdrifted to the meniscuses m, m, is caught on the circumferential facesof the rotating drums and the surface of the cast strip, and dischargedfrom the molten metal pool 3.

[0048] In this connection, in the method of the present invention,flaws, which are caused by the scum, exist in a portion of the caststrip in which the scum is being caught. Therefore, in many cases, thisportion of the cast strip is defective so that it is impossible tosupply this portion of the cast strip as a product.

[0049] However, flaws are usually generated and formed in a top portionand a tail portion of each coil-shaped thin cast strip, wherein thelength of the top portion and the length of the tail portion arerespectively about 2 to 4 m.

[0050] Therefore, these top and tail portions are defective portionswhich cannot become a product. Accordingly, when the scum is dischargedinto these defective portions in the process of casting, an additionaldeterioration of the yield is not caused.

[0051] Accordingly, it is preferable that “the time when castingcorresponding to one coil of thin cast strip has been completed”described in the method of the present invention is “the time whencasting of a product portion of the thin cast strip except for the abovedefective portions has been completed”.

[0052] In this connection, the scum may be discharged according to aquantity of the generated scum, that is, the scum may not be necessarilydischarged each time a casting corresponding to one coil has beencompleted.

[0053] Next, an example will be explained below.

EXAMPLE

[0054] A twin drum type continuous casting machine was used, wherein thediameter of each cooling drum was 1200 mm and the width was 1300 mm. Asan example of the present invention, molten metal of 180 ton wascontinuously cast according to the embodiment shown in FIGS. 2 and 3.

[0055] When casting corresponding to one coil was completed, the scumdrifted, due to a flow of gas, toward the circumferential faces of thecooling drums and was discharged from the molten metal pool.

[0056] In the comparative example, the conventional scum dams were used,however, the scum was not discharged. As a result, the ratio ofgeneration and formation of surface defects, which totally representsthe generation and formation of surface cracks and unevenness of gloss,of the comparative example was about five times as high as that of theembodiment of the present invention.

INDUSTRIAL APPLICABILITY

[0057] According to the present invention, in the method of casting athin cast strip by a twin drum type continuous casting machine andwinding the thin cast strip into a coil so as to manufacture a pluralityof coil-shaped thin cast strips, when casting corresponding to one coilof the thin cast strip has been completed, scum floating on a moltenmetal surface in a molten metal pool drifts and is collected at themeniscus, so that the scum can be made to adhere onto a surface of thecast strip and circumferential faces of the cooling drums and dischargedfrom the molten metal pool.

[0058] Therefore, according to the present invention, no scum isaccumulated even in the case of continuous casting performed over a longperiod of time, and cast strips of high quality can be manufactured.

1. A continuous casting method for manufacturing thin cast strips, inwhich a pair of scum dams extending in a drum width direction arrangedon both sides of a molten metal pouring nozzle are arranged by beingdipped in molten metal in molten metal pool formed by a pair of coolingdrums and a pair of side dams, a thin cast strip is cast while moltenmetal is being supplied into the molten metal pool, and the thin caststrip is wound into a coil so as to manufacture a plurality ofcoil-shaped thin cast strips, the continuous casting method formanufacturing thin cast strips comprising the step of pulling up thescum dams from the molten metal when casting work, corresponding to onecoil of the thin cast strip, is completed.
 2. A continuous castingmethod for manufacturing thin cast strips, in which a thin cast strip iscast while molten metal is being supplied into a molten metal poolformed by a pair of cooling drums and a pair of side dams, and the thincast strip is wound into a coil so as to manufacture a plurality ofcoil-shaped thin cast strips, the continuous casting method formanufacturing thin cast strips comprising the step of blowing gas onto amolten metal face in the molten metal pool toward one of the pair ofcooling drums or both of the pair of cooling drums when the castingwork, corresponding to one coil of the thin cast strip, is completed. 3.A continuous casting machine for manufacturing thin cast strips, inwhich a thin cast strip is cast while molten metal is being suppliedinto a molten metal pool formed by a pair of cooling drums and a pair ofside dams, and the thin cast strip is wound into a coil so as tomanufacture a plurality of coil-shaped thin cast strips, the continuouscasting machine for manufacturing thin cast strips comprising gasnozzles to blow gas, which are arranged at an upper central portion ofthe molten metal pool, being directed toward one or both of the pair ofcooling drums, to a molten metal face of the molten metal pool whencasting operation corresponding to one coil of the thin cast strip hasbeen completed.